1. Field of the Invention
The present invention relates to blanket clamping devices in which rubber blankets are clamped or tensioned by means of one or two clamping rails arranged in a clamping duct.
2. Description of the Related Art
In known devices for clamping the rubber blanket on the transfer cylinder of offset printing machines, the ends of the rubber blanket which are reinforced, for example, by means of strips or bars, are in engagement with clamping rails. In accordance with EP 0 060 492 A1, two clamping rails are mounted in the clamping duct of the transfer cylinder inclined at an angle relative to each other. For clamping the rubber blanket, the clamping rails are moved by means of tightening screws in direction toward the bottom of the clamping duct. The transfer cylinder may have several clamping ducts which are arranged distributed over the circumference thereof, wherein the two ends of a rubber blanket are clamped in two adjacent clamping ducts. Also known in the art are blanket clamping devices in which only one clamping rail is mounted in the clamping duct, wherein both ends of the rubber blanket are in engagement with the sides of the clamping rail (EP 0 099 275 B1).
The known blanket clamping devices have the disadvantage that the tightening screws may loosen and, consequently, the clamping rails may project out of the clamping duct and may damage the printing mechanism. This can also not be prevented by securing ledges which are screwed onto the clamping rails and cover the heads of the tightening screws.